Large regions of the Polar Oceans are covered by sea ice. The ice has a profound impact on the exchange of heat, momentum, and matter between the ocean and the atmosphere, on the solar albedo of the ocean, and on deep ocean circulation. Information about sea ice conditions are needed for ship navigation, fisheries, or oil and gazxs exploration, in geoand biophysical studies, and in climate research. In this chapter, methods of sea ice monitoring using synthetic aperture radar are addressed. The influence of sea ice properties such as surface roughness or volume structure on the observed radar signatures is explained, also considering environmental effects. We discuss advantages and limitations of different SAR configurations for sea ice observations. The use of SAR imagery for ice type discrimination is examined. The determination of other parameters such as ice drift, timing and length of the melt season, melt pond coverage, sea ice concentration, or extension of polynyas are briefly summarized. The usefulness of SAR data for validation and improvements of numerical models for simulating the dynamics of the sea ice cover is emphasized. © 2008 Springer Science+Business Media B.V.